1. remove NBU software if the client still alive? - not necessary to remove and you willneed the NetBackup software on the client if you have some need to restore from last full backup

2. remove it from any NBU configuration files?- I like to remove the client from the master server properties for client attributes - But all that is necessary is to remove client from any active/deactive policy it may be in

3. restart any NBU services?- No services need to be restarted

4. what should we prepare on this time in case for a furture restore if we have to?- I suggest changing the retention of the last full backup to the longest retention used in your environment.